1. Field of the Invention
The present invention relates to a fuel injection control apparatus for an internal combustion engine and a fuel injection control method for the internal combustion engine.
2. Description of Related Art
For fuel injection amount control for the internal combustion engine, a boost correction such as so-called over-temperature protection (OTP) boosting or power boosting is known to increase and correct the fuel injection amount more than a normal operating condition of the engine. The OTP boosting is a boost correction of the fuel injection amount that is performed to prevent overheating of an exhaust gas catalytic converter. When the fuel injection amount is boosted, exhaust gas temperature decreases by vaporization heat of fuel, and therefore the temperature of the exhaust gas catalytic converter can be decreased. On the other hand, the power boosting is a boost correction of the fuel injection amount that is performed to increase output torque. When air-fuel ratio of mixture is decreased to output air-fuel ratio through boosting of the fuel injection amount, the output torque can be increased.
The boost corrections described above are performed when the operating condition of the internal combustion engine is in a specific operating condition. For example, the OTP boosting may be performed in a high load and high speed operating condition, and the power boosting may be performed in a high load operating condition in which sudden acceleration is required. Here, a boost value of the fuel injection amount in the OTP boosting is referred to as an OTP boost value, and a boost value of the fuel injection amount in the power boosting is referred to as a power boost value.
Japanese Patent Application Publication No. 2003-343242 discloses a technique that obtains a basic value of estimated steady temperature of a catalyst in a steady operating condition of an internal combustion engine on the basis of engine speed and engine load and corrects the basic value in accordance with at least one of retarding degree of ignition timing, reflowing degree of exhaust gas into intake system, boosting degree of fuel injection amount in approximately full open of a throttle valve to obtain the estimated steady temperature of the catalyst.
When the OTP boost value in OTP boosting is excessively large with respect to the temperature of the exhaust gas catalytic converter, it may result in worsening of fuel economy or exhaust characteristic. Thus, when the OTP boosting is performed, the temperature of the exhaust gas catalytic converter is estimated, and the OTP boost value needs to be adjusted to the value in accordance with the estimated temperature.
Even in the case where the power boosting is performed, as in the case where the OTP boosting is performed, the temperature of exhaust gas decreases by the vaporization heat of fuel, and therefore the temperature of the exhaust gas catalytic converter decreases along with it. Thus, when the temperature of the exhaust gas catalytic converter is estimated during the power boosting, temperature decreasing amount for the exhaust gas catalytic converter caused by the power boosting usually needs to be considered.